The invention relates generally to highly heat-resistant positive resists based on oligomer polybenzoxazole precursors, polymer polybenzoxazole precursors, or mixtures thereof and diazoquinones and particularly to storage stable positive resists.
In highly temperature-resistant photoresists, which are needed for a cost-effective, direct structuring of organic insulating layers, hydroxypolyamides are used as soluble polybenzoxazole precursors. The polybenzoxazoles obtained from the hydroxypolyamides are distinguished by a high temperature resistance and low water absorption as well as by excellent electrical properties. The polybenzoxazoles can serve as etching masks in alkaline etching processes, and also as organic dielectrics in semiconductor production.
Photostructurable polybenzoxazole precursors may be used in positive and negative resists. In addition to the polymer precursor, the positive resists generally contain a photoactive component in the form of diazoquinone (see European Patent Specification 0 023 662, EP Published Patent Application 0 291 779 and German Published Patent Application 37 16 629), while the negative resists contain polymer precursors with cross-linkable, unsaturated groups (see European Patent Specification 0 041 677).
However, in both of the mentioned resist types, problems can occur with respect to storage stability. In the case of positive resists containing hydroxypolyamides, a polycondensation can take place in concentrated resist solutions; negative resists tend to polymerize because of the presence of unsaturated groups, such as acrylic and methylacrylic groups. In both resist types, this leads to an increase in viscosity and can result in a gel formation. Moreover, in positive resists, the photoactive component can be destroyed by terminal alkaline amino groups or by amine monomers and amide oligomers.
An object of the invention is to specify cost-effective, highly heat-resistant positive resists based on oligomer polybenzoxazole precursors, polymer polybenzoxazole precursors, or mixtures thereof and diazoquinones, in which the storage stability difficulties associated with these types of resists do not occur. The resist solutions should not only be sufficiently stable in storage, but also produce relief structures with a dimensional stability greater than 400.degree. C.